One of the biggest changes in our practical conservation work this year has been the way we tackle Giant Hogweed, one of the UK’s most damaging invasive plants. For many years, controlling Giant Hogweed has relied heavily on herbicide spraying. While effective, spraying requires repeated applications and uses significant quantities of chemicals, particularly along riverbanks where care must be taken to protect surrounding habitats. This year, we’ve taken a different approach.
Since the start of the 2026 invasive species season, our volunteers have dedicated 379 hours to Giant Hogweed control, with 189.5 hours – exactly half of that time – spent along the Murrayburn, one of the Water of Leith’s most important sources of reinfestation. During the first quarter of the financial year alone, 321.5 volunteer hours were spent tackling Giant Hogweed, almost double the time invested at the same point last year.
The increase reflects a move away from simply spraying plants towards physically digging them out before they flower and set seed. It’s more labour intensive, but our volunteers have risen to the challenge.
What has given us the confidence to change our approach is the completion of a five-year research partnership with Edinburgh Napier University. The study, carried out between 2018 and 2022, provided rare, real-world evidence that digging Giant Hogweed is just as effective as herbicide spraying in achieving long-term control, with no meaningful difference in outcomes. The findings have allowed us to dramatically reduce our reliance on chemicals. Compared with this time last year, we’ve reduced herbicide use by 85%, using 206 litres less chemical while still maintaining effective control of the plant.
The research also showed that the benefits extend far beyond removing one invasive species. Once Giant Hogweed is controlled, native vegetation begins to recover naturally, with plant species richness increasing by around 20% and riverbank habitats becoming more diverse and resilient—without the need for expensive replanting.
However, this isn’t a quick fix. Giant Hogweed produces thousands of seeds that can survive in the soil for many years. The study found that successful control requires consistent management over five to seven years, with regrowth expected at around 75% of treated sites as buried seeds continue to germinate. That means revisiting sites year after year, removing new plants before they have a chance to replenish the seed bank.
This is why our work on the Murrayburn is so important. By concentrating effort on one of the main upstream sources of Giant Hogweed, we’re reducing the number of seeds washing downstream and protecting the wider Water of Leith catchment. The research highlighted that controlling invasive species at a catchment scale is essential if long-term eradication is to be achieved
‘The Diggers’ dressed and ready for action